Method of producing hard cemented carbide composites



and lapping thereof in much the same manner as hardened and overtemperedsteel. By increasing the hardness and strength f the presiriteredmaterial, the diillculties which have previously precluded itssatisfactory grinding into ne razor edges is removed and advantage canbe taken of a condition of the material which permits of its beingworked into these shapes very much as steel iscustomarily fabricatedinto the usual razor blade.

. Accordingly, objects of my invention are to provide: a novel hardcemented carbide; a novel process for making a hard cemented carbide; a

Y novel hard cemented carbide razor blade; novel of control of thecomposite in the pre-sintered several hours.

and/or final sintered stage; the step in the process which comprisesincreasing the compacting pressure applied to the comxninuted compositeprevious to sintering; the step of oxidizing the binding metal duringmixing; the step of producing an oxide coating of the cementing mate-Arial around the hard carbide particles; and the employment of anauxiliary binding metal'in the process to provide temporary hardness, orany combination of these steps in the process.

Ihere are other objects of my invention which, together with theforegoing, will appear in the detailed description which is to.follow.

In practising my invention, I mix the hard f metal carbide and cementingmetal or metals in powdered form in Aa metal rolling barrel filled withmetal balls or rods. This is completed in Heretofore, it has been theprac.- tice during this operation to prevent oxidation of the powderedcementing metal by illling the barrel with water or a neutral orreducing gas. In accordance with my invention, I, quite the contrary,contemplate a slight oxidation of the cementing metal. Accordingly,during this mix-` ing, I heat the barrel slightly and introduce oxygenin order to slightly oxidizethe binding metal which thus forms an oxideillm around. the car-- bide particles.

Subsequently, on the application of further heat with a reducing agentas will be described hereinafter, the oxide illm will be re` duced aftercompacting and during the pre-sintering treatment will cement thecarbide producing a considerable increase in the hardness and strengthof the material. L Y

The degree of heat employed and the duration of this oxidizing treatmentwill vary with the materials used. I have found, however, that usingtungsten carbide, for example, as a hard carbide constituent and 10% byweight of metallic cobalt in powdered form as a cementing material thata barrel temperature of from 200 to 400 F. and

an oxidizing period of about an hour with theintroduction of threeliters of oxygen' at atmospheric pressure is sufilcient to producesatisfactory results.

economy although rectangular billets or other. forms can be used. Iemploy apressure 0f fr0!!! 60,000 to 200,000 pounds per square inch oreven A greater pressures, depending upon the materials used and the typeof blade which is to be made. In the usual practice, pressures of from10,000 to 60,000 pounds per square inch are used. As a means offurthering the even application of these high pressures, I have found itadvisable to employ a lubricant such as parailln or c amphor,- treatingthe powders with these materials in such carrying mediums as carbontetrachloride or benzene as is the common practice.

I may, if desired, employ an auxiliarymetal of lower melting point thanthe cementing metal or metals, although this is not always necessary asthe other steps of my process are sufilcient'for the production .ofblades of some types. vIn that use, I generally introduce the auxiliarymetal in A powdered form atthe same time as the cementing metal, but itcan be added either before or after the oxidizing process just describeddepending upon the type of the auxiliary metal which is used. Thefunction of this auxiliary metal is to cement the particles of hardcarbide and the rparticles or pelliclesof the cementing metal or beused, In selecting them, care must be exeri cised to combine themsuitably with the true cementing metals if they are to remain as analloy of the ultimate metal matrix. Copper can be used satisfactorilywith nickel or cobalt as an auxiliary metal in a cemented tungstencarbide composition for example. In making a composition of this kind Iwould, for example, mix the following powdered components in the mannerwhich has been described, adding the copper powder after the oxidizingperiod: tungsten carbide, by weight; cobalt or nickel, 7% by weight;copper. 3% by weight. v

I may, on the other hand, employ an auxiliary metal such as silver inconjunction with a true cementing metal such as nickel with which itdoesnot alloy. Or under some circumstances, I may use zinc which meltsat al low temperature and is volatile before the melting point of 'suchmetals as cobaltor nickel.

A suitable composition entailing the use of silver would be: tungstencarbide, 87% by weight; nickel, 1% by weight; silver, 6% by weight. Ifzinc is usedl aisuitable composition `would be: titanium carbide, 87%;nickel, 9%;

zine, 4%. n should be understood 'that these examples are given forillustration purposes only and that the scope of my invention is not-limited to beused depends upon the character of the blade which is tobe produced, the composition of the hard cemented carbide material whichhas been selected and the auxiliary metal, if any, which is employed inthe production of a suitable pre-sintered state of hardness, strengthand cohesion.

As the suitable metals have a wide variety of melting points, I preferan upper limit of just below the melting point of the true cementingmetal or alloy. For example, with a cobalt ce- 50 f' pounlds per squareinch depending upon the in the composite.

to 200,000. pounds per square inch depending upon the material used, andapplying a presintering temperature just below the melting point of thecementlng metal and reducing the oxides formed 10. In the presinteringprocess 'for producing hard cemented carbides, the steps of controllingthe hardness of the presintered composite which comprises mixingtungsten carbide and powdered metallic cobalt, heating the composite inan oxidizing atmosphere, -compacting the. composite at a pressure above60,000 pounds per square -inch depending upon the metals used, andapplying' a presintering temperature just vbelow the melting point ofthe metallic cobalt and reducing' the oxides formed in the composite.

11. In the presinteri'ng process for producing Vhard cemented carbides,the steps of controlling the hardness of the presintered composite whichcomprises mixing a, hard metal carbide and a cementing metal in powderedform, heating the I'. composite to a temperature of 200 to 400 F. in anlso oxidizing atmosphere, compacting the composite at a pressure above60,000 pounds per square inch, and applying a presintering temperaturejust below the melting point of the cementing metal .and reducing theoxides formed in the composite.

l2.` In the presintering process for producing hard cemented carbides,the-steps of controlling the hardness of the presintered compositewhichcomprises mixing a hard metal carbide and a rst cementing metal inpowdered form, heating the composite in an oxidizing atmosphere,compacting the composite at a, pressure above 60,000

pounds per square inch depending upon the metals used, cementing themetals with a powdered metal added with the rst cementing metal andhaving a lower melting point than the rst cementing metal for transientbinding before working the composite, and applying a presinteringtemperature just below the melting point of the rst cementing metal andreducing the oxides formed in the composite.

13. In the presntering process for producingV hard cemented carbides,the steps of controlling the hardness of the presintered composite whichcomprises mixing a hard metal carbide and a rst cementing metal inpowdered form, heating the composite in an oxidizing atmosphere,compacting the composite at a pressure above 60,000

metals used, adding together with the iirst cementing metal a metalwhich alloys withlthe first cementng metal and melts atjf'a-lowertemperature to bind the composite forworking, and applying apresintering temperature just below the melting point of the ilrstcementlng metal and reducing the oxides formed'jin ythe composite.

14. In.the presintering process for producing hard cemented carbides,the steps of controlling' the hardness of the'presintered compositewhich comprises mixing a hard metal carbide and a rst cementing metal inpowdered form, heating the composite in an oxidizing atmosphere,compacting the composite at a pressure above 60,000 pounds persquareinch depending upon the metals used, adding together with the rstcementing metal a cementing metal whichA volatilizes below the meltingpoint of the rst cementing metal, and applying a presintering tempera-yture just below the' melting point ofthe first cementing metal andreducing the oxidesrformed in the composite.

15. In the prcsintering process .foi-1; producingy hard cementedcarbides, the steps offontrolling the hardness of the presinteredcomposite which comprises mixing a hard metalk Acarbide as tungstencarbide 94% and a first cementing metal in powdered form as cobalt 6%,heatingthe composite in an oxidizing atmosphere, compacting they fcomposite at a pressure above 60,00054 pounds per square inch dependingupon the. metals used, cemcnting the metals with a powdered metal addedwith the iirst eementing metal and having a.y

lower melting point than the rst cenienting metal for transient bindingbefore'working the pounds per square inch, and applying a presinteringtemperature just below the melting point of the cementing metal andreducing the `oxides formed in the composite.

GREGORY J. COMSTOCK.

